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[mediawiki.git] / includes / filebackend / lockmanager / DBLockManager.php

<?php
/**
 * Version of LockManager based on using DB table locks.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup LockManager
 */

/**
 * Version of LockManager based on using named/row DB locks.
 *
 * This is meant for multi-wiki systems that may share files.
 *
 * All lock requests for a resource, identified by a hash string, will map
 * to one bucket. Each bucket maps to one or several peer DBs, each on their
 * own server, all having the filelocks.sql tables (with row-level locking).
 * A majority of peer DBs must agree for a lock to be acquired.
 *
 * Caching is used to avoid hitting servers that are down.
 *
 * @ingroup LockManager
 * @since 1.19
 */
abstract class DBLockManager extends QuorumLockManager {
        /** @var array Map of DB names to server config */
        protected $dbServers; // (DB name => server config array)
        /** @var BagOStuff */
        protected $statusCache;

        protected $lockExpiry; // integer number of seconds
        protected $safeDelay; // integer number of seconds

        protected $session = 0; // random integer
        /** @var array Map Database connections (DB name => Database) */
        protected $conns = array();

        /**
         * Construct a new instance from configuration.
         *
         * @param array $config Paramaters include:
         *   - dbServers   : Associative array of DB names to server configuration.
         *                   Configuration is an associative array that includes:
         *                     - host        : DB server name
         *                     - dbname      : DB name
         *                     - type        : DB type (mysql,postgres,...)
         *                     - user        : DB user
         *                     - password    : DB user password
         *                     - tablePrefix : DB table prefix
         *                     - flags       : DB flags (see DatabaseBase)
         *   - dbsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
         *                   each having an odd-numbered list of DB names (peers) as values.
         *                   Any DB named 'localDBMaster' will automatically use the DB master
         *                   settings for this wiki (without the need for a dbServers entry).
         *                   Only use 'localDBMaster' if the domain is a valid wiki ID.
         *   - lockExpiry  : Lock timeout (seconds) for dropped connections. [optional]
         *                   This tells the DB server how long to wait before assuming
         *                   connection failure and releasing all the locks for a session.
         */
        public function __construct( array $config ) {
                parent::__construct( $config );

                $this->dbServers = isset( $config['dbServers'] )
                        ? $config['dbServers']
                        : array(); // likely just using 'localDBMaster'
                // Sanitize srvsByBucket config to prevent PHP errors
                $this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
                $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive

                if ( isset( $config['lockExpiry'] ) ) {
                        $this->lockExpiry = $config['lockExpiry'];
                } else {
                        $met = ini_get( 'max_execution_time' );
                        $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
                }
                $this->safeDelay = ( $this->lockExpiry <= 0 )
                        ? 60 // pick a safe-ish number to match DB timeout default
                        : $this->lockExpiry; // cover worst case

                foreach ( $this->srvsByBucket as $bucket ) {
                        if ( count( $bucket ) > 1 ) { // multiple peers
                                // Tracks peers that couldn't be queried recently to avoid lengthy
                                // connection timeouts. This is useless if each bucket has one peer.
                                try {
                                        $this->statusCache = ObjectCache::newAccelerator( array() );
                                } catch ( MWException $e ) {
                                        trigger_error( __CLASS__ .
                                                " using multiple DB peers without apc, xcache, or wincache." );
                                }
                                break;
                        }
                }

                $this->session = wfRandomString( 31 );
        }

        // @todo change this code to work in one batch
        protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
                $status = Status::newGood();
                foreach ( $pathsByType as $type => $paths ) {
                        $status->merge( $this->doGetLocksOnServer( $lockSrv, $paths, $type ) );
                }

                return $status;
        }

        protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
                return Status::newGood();
        }

        /**
         * @see QuorumLockManager::isServerUp()
         * @param string $lockSrv
         * @return bool
         */
        protected function isServerUp( $lockSrv ) {
                if ( !$this->cacheCheckFailures( $lockSrv ) ) {
                        return false; // recent failure to connect
                }
                try {
                        $this->getConnection( $lockSrv );
                } catch ( DBError $e ) {
                        $this->cacheRecordFailure( $lockSrv );

                        return false; // failed to connect
                }

                return true;
        }

        /**
         * Get (or reuse) a connection to a lock DB
         *
         * @param string $lockDb
         * @return DatabaseBase
         * @throws DBError
         */
        protected function getConnection( $lockDb ) {
                if ( !isset( $this->conns[$lockDb] ) ) {
                        $db = null;
                        if ( $lockDb === 'localDBMaster' ) {
                                $lb = wfGetLBFactory()->getMainLB( $this->domain );
                                $db = $lb->getConnection( DB_MASTER, array(), $this->domain );
                        } elseif ( isset( $this->dbServers[$lockDb] ) ) {
                                $config = $this->dbServers[$lockDb];
                                $db = DatabaseBase::factory( $config['type'], $config );
                        }
                        if ( !$db ) {
                                return null; // config error?
                        }
                        $this->conns[$lockDb] = $db;
                        $this->conns[$lockDb]->clearFlag( DBO_TRX );
                        # If the connection drops, try to avoid letting the DB rollback
                        # and release the locks before the file operations are finished.
                        # This won't handle the case of DB server restarts however.
                        $options = array();
                        if ( $this->lockExpiry > 0 ) {
                                $options['connTimeout'] = $this->lockExpiry;
                        }
                        $this->conns[$lockDb]->setSessionOptions( $options );
                        $this->initConnection( $lockDb, $this->conns[$lockDb] );
                }
                if ( !$this->conns[$lockDb]->trxLevel() ) {
                        $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
                }

                return $this->conns[$lockDb];
        }

        /**
         * Do additional initialization for new lock DB connection
         *
         * @param string $lockDb
         * @param DatabaseBase $db
         * @throws DBError
         */
        protected function initConnection( $lockDb, DatabaseBase $db ) {
        }

        /**
         * Checks if the DB has not recently had connection/query errors.
         * This just avoids wasting time on doomed connection attempts.
         *
         * @param string $lockDb
         * @return bool
         */
        protected function cacheCheckFailures( $lockDb ) {
                return ( $this->statusCache && $this->safeDelay > 0 )
                        ? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
                        : true;
        }

        /**
         * Log a lock request failure to the cache
         *
         * @param string $lockDb
         * @return bool Success
         */
        protected function cacheRecordFailure( $lockDb ) {
                return ( $this->statusCache && $this->safeDelay > 0 )
                        ? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
                        : true;
        }

        /**
         * Get a cache key for recent query misses for a DB
         *
         * @param string $lockDb
         * @return string
         */
        protected function getMissKey( $lockDb ) {
                $lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
                return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
        }

        /**
         * Make sure remaining locks get cleared for sanity
         */
        function __destruct() {
                $this->releaseAllLocks();
                foreach ( $this->conns as $db ) {
                        $db->close();
                }
        }
}

/**
 * MySQL version of DBLockManager that supports shared locks.
 * All locks are non-blocking, which avoids deadlocks.
 *
 * @ingroup LockManager
 */
class MySqlLockManager extends DBLockManager {
        /** @var array Mapping of lock types to the type actually used */
        protected $lockTypeMap = array(
                self::LOCK_SH => self::LOCK_SH,
                self::LOCK_UW => self::LOCK_SH,
                self::LOCK_EX => self::LOCK_EX
        );

        /**
         * @param string $lockDb
         * @param DatabaseBase $db
         */
        protected function initConnection( $lockDb, DatabaseBase $db ) {
                # Let this transaction see lock rows from other transactions
                $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
        }

        /**
         * Get a connection to a lock DB and acquire locks on $paths.
         * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
         *
         * @see DBLockManager::getLocksOnServer()
         * @param string $lockSrv
         * @param array $paths
         * @param string $type
         * @return Status
         */
        protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
                $status = Status::newGood();

                $db = $this->getConnection( $lockSrv ); // checked in isServerUp()

                $keys = array(); // list of hash keys for the paths
                $data = array(); // list of rows to insert
                $checkEXKeys = array(); // list of hash keys that this has no EX lock on
                # Build up values for INSERT clause
                foreach ( $paths as $path ) {
                        $key = $this->sha1Base36Absolute( $path );
                        $keys[] = $key;
                        $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
                        if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
                                $checkEXKeys[] = $key;
                        }
                }

                # Block new writers (both EX and SH locks leave entries here)...
                $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
                # Actually do the locking queries...
                if ( $type == self::LOCK_SH ) { // reader locks
                        $blocked = false;
                        # Bail if there are any existing writers...
                        if ( count( $checkEXKeys ) ) {
                                $blocked = $db->selectField( 'filelocks_exclusive', '1',
                                        array( 'fle_key' => $checkEXKeys ),
                                        __METHOD__
                                );
                        }
                        # Other prospective writers that haven't yet updated filelocks_exclusive
                        # will recheck filelocks_shared after doing so and bail due to this entry.
                } else { // writer locks
                        $encSession = $db->addQuotes( $this->session );
                        # Bail if there are any existing writers...
                        # This may detect readers, but the safe check for them is below.
                        # Note: if two writers come at the same time, both bail :)
                        $blocked = $db->selectField( 'filelocks_shared', '1',
                                array( 'fls_key' => $keys, "fls_session != $encSession" ),
                                __METHOD__
                        );
                        if ( !$blocked ) {
                                # Build up values for INSERT clause
                                $data = array();
                                foreach ( $keys as $key ) {
                                        $data[] = array( 'fle_key' => $key );
                                }
                                # Block new readers/writers...
                                $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
                                # Bail if there are any existing readers...
                                $blocked = $db->selectField( 'filelocks_shared', '1',
                                        array( 'fls_key' => $keys, "fls_session != $encSession" ),
                                        __METHOD__
                                );
                        }
                }

                if ( $blocked ) {
                        foreach ( $paths as $path ) {
                                $status->fatal( 'lockmanager-fail-acquirelock', $path );
                        }
                }

                return $status;
        }

        /**
         * @see QuorumLockManager::releaseAllLocks()
         * @return Status
         */
        protected function releaseAllLocks() {
                $status = Status::newGood();

                foreach ( $this->conns as $lockDb => $db ) {
                        if ( $db->trxLevel() ) { // in transaction
                                try {
                                        $db->rollback( __METHOD__ ); // finish transaction and kill any rows
                                } catch ( DBError $e ) {
                                        $status->fatal( 'lockmanager-fail-db-release', $lockDb );
                                }
                        }
                }

                return $status;
        }
}

/**
 * PostgreSQL version of DBLockManager that supports shared locks.
 * All locks are non-blocking, which avoids deadlocks.
 *
 * @ingroup LockManager
 */
class PostgreSqlLockManager extends DBLockManager {
        /** @var array Mapping of lock types to the type actually used */
        protected $lockTypeMap = array(
                self::LOCK_SH => self::LOCK_SH,
                self::LOCK_UW => self::LOCK_SH,
                self::LOCK_EX => self::LOCK_EX
        );

        protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
                $status = Status::newGood();
                if ( !count( $paths ) ) {
                        return $status; // nothing to lock
                }

                $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
                $bigints = array_unique( array_map(
                        function ( $key ) {
                                return wfBaseConvert( substr( $key, 0, 15 ), 16, 10 );
                        },
                        array_map( array( $this, 'sha1Base16Absolute' ), $paths )
                ) );

                // Try to acquire all the locks...
                $fields = array();
                foreach ( $bigints as $bigint ) {
                        $fields[] = ( $type == self::LOCK_SH )
                                ? "pg_try_advisory_lock_shared({$db->addQuotes( $bigint )}) AS K$bigint"
                                : "pg_try_advisory_lock({$db->addQuotes( $bigint )}) AS K$bigint";
                }
                $res = $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
                $row = (array)$res->fetchObject();

                if ( in_array( 'f', $row ) ) {
                        // Release any acquired locks if some could not be acquired...
                        $fields = array();
                        foreach ( $row as $kbigint => $ok ) {
                                if ( $ok === 't' ) { // locked
                                        $bigint = substr( $kbigint, 1 ); // strip off the "K"
                                        $fields[] = ( $type == self::LOCK_SH )
                                                ? "pg_advisory_unlock_shared({$db->addQuotes( $bigint )})"
                                                : "pg_advisory_unlock({$db->addQuotes( $bigint )})";
                                }
                        }
                        if ( count( $fields ) ) {
                                $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
                        }
                        foreach ( $paths as $path ) {
                                $status->fatal( 'lockmanager-fail-acquirelock', $path );
                        }
                }

                return $status;
        }

        /**
         * @see QuorumLockManager::releaseAllLocks()
         * @return Status
         */
        protected function releaseAllLocks() {
                $status = Status::newGood();

                foreach ( $this->conns as $lockDb => $db ) {
                        try {
                                $db->query( "SELECT pg_advisory_unlock_all()", __METHOD__ );
                        } catch ( DBError $e ) {
                                $status->fatal( 'lockmanager-fail-db-release', $lockDb );
                        }
                }

                return $status;
        }
}